In some networks, for example, in a wireless local area network (WLAN), to avoid interference caused by a collision during data transmission, a carrier sense multiple access with collision avoidance (CSMA/CA) channel access mechanism is used. According to the CSMA/CA mechanism, when a station (STA) or an access point (AP) senses that a strength of a Wi-Fi signal on a channel is greater than −82 dBm or senses that a strength of any non-Wi-Fi signal on the channel is greater than −62 dBm, the STA or the AP determines that the current channel is in a busy state and sends no signal to avoid a collision. The industry considers that in a broad sense, a STA includes an AP and a non-AP STA, and that in a narrow sense, a STA means a non-AP STA. If a STA does not specifically mean an AP, a collective term STA or station is usually used. If a STA may mean an AP, terms AP and non-AP STA are used for distinguishing. In this specification, a non-AP STA may be referred to as a STA.
With development of communications technologies, a concept of spatial reuse (SR) is introduced to increase a system throughput in a high-density scenario. In a specific scenario or under a specific condition, two or more stations or APs are allowed to use time-frequency resources that are the same or partially same (it may be simply understood as using a same channel within a same time period) for transmission. It may be understood as follows: When a local basic service set (BSS) station or AP senses that there is a signal from an overlapping basis service set (OBSS) on a current channel, if a strength of the signal is greater than −82 dBm but less than an OBSS packet detection level (OBSS PD), an OBSS clear channel assessment (OBSS CCA) value, or a spatial reuse clear channel assessment (SR CCA) value, the local BSS station or AP may use a same channel through a specific means (for example, adjusting a transmit power) under a specific condition (for example, ongoing OBSS communication is not affected) to perform spatial reuse link transmission. Generally, the OBSS PD level needs to be greater than −82 dBm and less than −62 dBm. For example, as shown in FIG. 1, at the same time when an access point AP1 sends downlink data to a STA1 (a link between the AP1 and the STA1 may be referred to as a primary link), a STA2 uses all or some of time-frequency resources of the primary link to transmit uplink data to an access point AP2 (a link between the AP2 and the STA2 may be referred to as a spatial reuse link). The primary link and the spatial reuse link are relative concepts. An intersection of transmission time exists between the primary link and the spatial reuse link, or a transmission time of the spatial reuse link is a part of a transmission time of the primary link. For another link B that starts data transmission within a transmission time of a link A, if a transmit end station of the link B is within an effective communication distance between a transmit end station and a receive end station of the link A, and the link B uses all or some of time-frequency resources of the link A, the link A is referred to as the primary link of the link B, and correspondingly, the link B is the spatial reuse link of the link A. Generally, the primary link may be an uplink transmission link (that is, a transmission link from a STA to an AP), or may be a downlink transmission link (that is, a transmission link from an AP to a STA). FIG. 1 is a scenario in which the primary link is a downlink transmission link. The spatial reuse link may also be an uplink transmission link or a downlink transmission link. In FIG. 1, the spatial reuse link being an uplink transmission link is used as an example for demonstration, and the spatial reuse link is usually located in a BSS different from that of the primary link. Data packets of different BSSs usually carry different BSS identities. A BSS identity may be a BSS color located in a preamble signaling field of a data packet physical layer protocol data unit (PPDU), may be a BSS identifier (BSSID) in an address field in a MAC frame header carried in the PPDU, or may be presented in another form. A BSS from which the data packet is may be known by identifying the BSS identity.
At present, an effective determining mechanism for using the spatial reuse link is required, to reduce interference between the primary link and the spatial reuse link and improve transmission quality.